The prior art on the grafting of monomers onto fluoropolymers to make grafted polymers deals with polymers having grafts throughout the bulk of the material.
The synthesis of graft fluoropolymers during the polymerization process is known. For example, Kawashima et al. in U.S. Pat. No. 4,472,557 and Inoue et al. in U.S. Pat. No. 4,910,258 disclose the grafting of a crystalline fluoropolymer segment onto an elastomeric fluoropolymer backbone containing peroxy groups. As a further example, Tatemoto et al. in U.S. Pat. No. 4,158,678 disclose a segmented polymer prepared by polymerizing the first segment in the presence of an iodinated compound which donates terminal iodine to the first segment, permitting the addition of a second polymer segment of different composition. In both of these approaches, the grafted segments are polymeric and are attached to essentially all of the backbone molecules or starting segments.
Buning in U.S. Pat. No. 4,151,225 discloses a process for preparing a graft polymer of polyvinylidene fluoride (PVDF) wherein the PVDF has grafted thereon a polymer of an ethylenically unsaturated compound. This process involves the penetration of a monomer and a radical forming catalyst into the PVDF powder or granules, followed by polymerizing said monomer. Consequently, the PVDF is converted to the graft copolymer uniformly throughout its bulk. Example 1 of Buning shows the grafting of methacrylic acid methyl ester onto PVDF. After subtracting the weight of material extracted from the graft copolymer obtained, the weight of graft material added by the grafting process is about 34 wt % based on the original weight of the PVDF, illustrating the mass increase that can be realized in a bulk grafting process using a polymerizable grafting compound.
Jakabhazy et al. in U.S. Pat. No. 4,278,777 discloses a method of grafting a vinyl monomer onto a polymer having an aliphatic carbon-hydrogen group. This method comprises the swelling of the polymer with a solvent which will effect swelling, though typically not dissolution, with resultant grafting of the monomer onto the polymer throughout the bulk of the polymer, using a polymerization initiator to effect the graft.
Processes typified by those of Jakabhazy et al. and of Buning are not readily adaptable to polymers which are not easily swollen, such as copolymers of ethylene and tetrafluoroethylene and perhalogenated polymers. Furthermore, these processes produce bulk modification which may not be necessary or desirable.
It is sometimes desired to have composite structures of certain dissimilar materials, for example, a fluoropolymer and a polyamide or a polyester elastomer, to take advantage of certain properties of each, or to adhere a fluoropolymer to a metal to provide the metal surface with fluoropolymer characteristics.